A tachometer is a gauge that is part of a vehicle's instrumentation panel that displays a value of engine speed usually in revolutions per minute (RPM). In some implementations, a source of engine speed (e.g., crankshaft or camshaft position sensor) can be directly wired to the instrumentation panel that houses the tachometer. In other implementations, engine speed can be computed via an engine control module (ECM) based on information derived from either the crankshaft or camshaft speed sensor and an engine speed signal can be indirectly sent to the tachometer via serial data communication (e.g., via a controller area network (CAN) bus). Traditionally engine speed was displayed on a calibrated analogue dial that includes a needle fixed about a point that is directed to one of a plurality of numerical indications, i.e., 1000 RPM, 2000 RPM, 4000 RPM, and others. More recently, digital tachometers have become the state of the art for presenting engine speed.
Tachometers can allow the driver to visually assess operating speed of the engine, and assist the driver in selecting appropriate throttle and gear settings for the driving conditions. A driver of the automobile reads the tachometer to determine whether or not to shift gears or adjust the speed of the automobile. The driver should shift gears at selected engine speeds to extract maximum power from the engine and achieve maximum vehicle speed. Shifting to a higher transmission gear (or upshifting) too early often results in a loss of power and causes reduced acceleration or even stalling. Upshifting too late may result in over-revving the engine, that is, reaching an engine speed greater than a maximum recommended speed, which can cause damage to the engine or other portions of the drive train. Shifting to a lower transmission gear (or downshifting) at the wrong time often causes over-revving of the engine, which is commonly called “Redlining” the engine. Redlining may damage the engine. Unfortunately, it is often difficult to be able to shift at an appropriate time.
When the engine of the vehicle responds to the driver of the vehicle depressing the accelerator (e.g., while driving or when the vehicle is in park or neutral), this causes a corresponding response at the tachometer that can be viewed by the driver. In addition, events such as shifting gears can also cause a response at the tachometer to change. In most cases, the driver can also hear the response of the engine as the accelerator is depressed or when gears are shifted. In an ideal operating scenario, the response of the tachometer would match or be synchronized with the response of the vehicle to the acceleration or gear shift. For example, the tachometer needle or display should begin moving as soon as engine speed is transitioning since a synchronized engine sound and tachometer can greatly improve perception of powertrain performance.
However, in a real vehicle, there are many sources of delay in the signal path between the sensors that measure engine speed (or source of engine speed) and the tachometer (of the instrument panel) that displays an indication of rpm. These sources of delay cause the response that is presented on the tachometer to be out of synchronization with (or lag) the response of the vehicle to the acceleration or gear shift. For instance, some sources of the delayed response at the tachometer can include: delay in the engine's response to the driver interacting with the accelerator (or gear shifter); delay associated with an engine speed determination in an engine control module (ECM); delays associated with vehicle communication systems such as a high-speed controller area network (CAN) bus and a low-speed CAN bus; delays associated with a body control module (BCM); delay associated with internal signal processing by the instrument panel (IP); delay associated with dead-band filtering in the IP (calibration); delay associated with displaying the RPM indication at the tachometer, etc. As such, there are many sources that can contribute to a delayed response of the tachometer. A delayed tachometer response can contribute to negative perception by the user that the engine and/or transmission may be sluggish.
There is a need for tachometers that can provide improved performance and that can improve the user's perception of powertrain performance by mitigating communication delays between source of engine speed and the tachometer. There is a need for tachometer s that exhibit improved responsiveness despite many sources of delay that exist in a signal path between the tachometer and the sensors that measure engine speed. It would be desirable to provide a tachometer that generates an engine speed signal with reduced response delay so that the tachometer output at an instrumentation panel more closely matches that actual engine speed. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.